In his first-ever interview, the sole Australian survivor of the Waco siege has revealed to 60 Minutes what really took place during the 51-day stand-off, and why he believes crazed cult leader David Koresh will one day return to Earth as the son of God.

Marriage bill 'won't pass' if changes made

Labor has warned that changing a bill to legalise same-sex marriage at this stage of the process will likely doom its passage through parliament.

Frontbencher Tony Burke told MPs that if there is a dispute between what the lower and upper houses agree to, there is a real chance the changes could be stalled.

A number of government conservatives, as well as the Greens, have indicated they will be introducing amendments before the legislation gets to a final vote.

"If we get to the end of this year ... and we still don't get it done, the Australian people will have every right to be deeply frustrated and sick to death of this place," Mr Burke said on Tuesday, day two of debate on the legislation.

"There will be some amendments that will have a level merit, but to contemplate this not getting done is truly unthinkable."

Cabinet minister Peter Dutton has already conceded it will be "near impossible" to pass any of them, given the numbers in the House of Representatives.

Mr Burke, whose western Sydney electorate had the second-highest 'no' vote in the postal survey, will oppose any proposed change but agree to the bill itself.

Related Articles

He believes he needs to stand up for all kinds of discrimination, especially coming from an area that knows what it's like to be in a minority.

Senior Liberal Christopher Pyne, a long-time supporter of same-sex marriage, said he won't support any unnecessary amendments.

He insists the private bill, which the Senate passed last week, protects religious freedom in Australia.

"Acts of parliament should not contain superfluous clauses, especially those based on the opinion that Australia's laws don't adequately protect the religious freedoms that we have cherished since federation," Mr Pyne said.

It would be a hypocritical to deny the equal right of a civil marriage because of restrictions that apply to holy matrimony, he said.

"We don't deny civil marriage to infertile couples or divorcees, even though these two are traditional impediments to Christian marriage," he said.

A number of MPs revealed more personal stories during debate on Thursday, including Liberal and committed Catholic Andrew Wallace who spoke of his shock when he found out his daughter was gay.

In a powerful speech, Labor's Linda Burney offered a tear-filled tribute to her late gay son Binni, who died six weeks ago.

Tears were also shed by independent MP Andrew Wilkie, who declared the time for talking was over and demanded Australia "just do this thing".

Liberal backbencher Ian Goodenough doesn't believe the legislation has adequate safeguards for what he labelled "the most significant and radical social change in our nation's history ... even prior to European settlement".

He thinks the impact of the legislation on the budget has not been fully assessed and will have consequences on Australia's finances.

"There has not been sufficient debate about the consequential costs to society of making this change," Mr Goodenough said.

"Ultimately it's the taxpayers of Australia which will bear the cost."

Regardless, he will be voting 'yes' in line with the voting majority of its electorate.

Members of Australian Christians for Marriage Equality were in Canberra on Tuesday to lobby MPs against proposed amendments, including exemptions for civil celebrants, small businesses and religious charities, and separate definitions for men and women who get married and marriage between two people.

Debate will continue until midnight Tuesday, with dozens of MPs still slated to speak.